In general, a vacuum cleaner is an appliance for cleaning floors, carpets placed on floors, or the like by sucking air containing foreign substances using an air suction device, which includes a motor and a fan mounted inside the main body of the cleaner in order to generate air suction force, removing and collecting the foreign substances from the sucked air, and discharging purified air, from which the foreign substances have been removed, outside the main body of the cleaner.
Such a vacuum cleaner may be classified into a manual vacuum cleaner, which is directly manipulated by a user, and a robot cleaner, which performs cleaning autonomously without a user's manipulation.
The robot cleaner comprises a suction device mounted therein, which includes a motor and a fan. Because the size of the robot cleaner is limited, the size of the motor is also limited. That is, only a small motor may be mounted inside the robot cleaner.
Upon rotation of the fan, the rotating shaft of the small motor may move axially (that is, in the forward and rearward direction of the motor) a predetermined distance due to the thrust generated by the rotation of the fan. That is, the rotating shaft of the small motor may move axially a predetermined distance within the range of end play.
However, if the rotating shaft of the motor moves axially within the range of end play upon rotation of the fan, the distance between the fan and a cover mounted in front of the fan may be changed, which causes the dispersion of suction force.
The robot cleaner autonomously travels in an area to be cleaned, and sucks foreign substances such as, for example, dust from the floor. In addition, the robot cleaner may include various sensors (for example, an obstacle sensor) in order to avoid obstacles or walls located within the working area.
The obstacle sensor may be configured to emit infrared light and receive the infrared light reflected from an object, thereby measuring the distance to obstacles or walls located ahead of the sensor. That is, the obstacle sensor may include an infrared sensor.
For instance, the infrared sensor may include a light-emitting unit (a transmission unit) and a light-receiving unit (a reception unit), and may enable measurement of the distance between the infrared sensor and an obstacle located ahead of the infrared sensor using the time taken for the infrared light emitted from the light-emitting unit to be received by the light-receiving unit after being reflected from the obstacle.
The obstacle sensor is exposed to direct solar radiation, which progresses toward the obstacle sensor from outside the robot cleaner.
However, if the obstacle sensor receives direct solar radiation (for example, visible light) other than the light emitted from the light-emitting unit of the infrared sensor, there is a high probability of the obstacle sensor malfunctioning.
In order to solve this problem, it may be considered to form the outer surface of the robot cleaner, which covers the obstacle sensor, using a material that allows only infrared light to pass therethrough. However, there is a problem in that such a material, which allows only infrared light to pass therethrough, is more expensive than a commonly used plastic material.
Further, if the material that allows only infrared light to pass therethrough is scratched, there is a problem in that the obstacle sensor cannot accurately receive the light (that is, infrared light) incident thereon.
In other words, a scratch formed on the surface of a material that allows only infrared light to pass therethrough may cause a malfunction of the obstacle sensor.